Masonry Magazine February 1996 Page. 43
Portland Cement Association
pca
TROWEL TIPS
an aid to the masonry industry
Workmanship
Part II, Imparting Quality to Masonry
Introduction
The first of this two part series on workmanship (Trowel Tips: Workmanship Part I, Preparing for Quality, IS 245) focused on the preparation, teamwork, and support that must be provided so that a mason can construct quality masonry structures. This document examines important aspects of hands-on mason skills that are employed in the actual on-site fabrication of masonry. Both are necessary to realize the goal of completing masonry construction that attains the level of strength, durability, and aesthetic appeal expected of masonry. Certain basic skills are required in addition to effective interaction between the mason constructing the masonry, other members of the masonry contractors support crew, and the project construction team.
Construction
Mortar Consistency. The need for the combination of skill and teamwork is perhaps best illustrated by examining the on-site establishment of the working consistency of freshly mixed mortar. Mortar should be mixed with the maximum amount of water that is consistent with satisfactory workability. The mason can best evaluate the optimum consistency of the freshly mixed mortar as he uses the mortar to place units under prevailing environmental conditions. Certainly, a proper evaluation of the mortar consistency by the mason requires a general knowledge of masonry materials, experience with the specific masonry materials, and an understanding of how prevailing environmental conditions affect masonry construction. However, unless that evaluation is effectively conveyed to the individual mixing the mortar and appropriate adjustments made to the mortar mix, the mason's evaluation is pointless. Knowledge, skill, communication, and teamwork are required to establish and maintain optimum consistency of freshly mixed mortar.
Retempering. Fresh mortar should be prepared at the ate used, so that its workability will remain about the same hroughout the day. Mortar that has been mixed but not used immediately tends to dry out and stiffen. Loss of water by absorption and evaporation on a dry day can be reduced by wetting the mortarboard and covering the mortar in the nortar box, wheelbarrow, or tub.
Mortar that has stiffened due to evaporation should be retempered to restore workability by adding water and thoroughly remixing (Fig. 1). Although small additions of water may slightly reduce the compressive strength of the mortar, the result is acceptable. Masonry built using plastic mortar has a better bond strength than masonry built using dry, stiff mortar.
Mortar that has stiffened because of hydration should be discarded. Since it is difficult to determine by sight or feel whether mortar stiffening is due to evaporation or to setting of the cement, the most practical method of determining the suitability of mortar is on the basis of time elapsed after mixing. Mortar should be used within 2-1/2 hours after mixing.
Fig. 1. Retempering restores workability.
Portland Cement Association, 1994
MASONRY JANUARY/FEBRUARY, 1996 43